It has long been recognized in the sawmill industry that the predominant cause of lumber loss in the conversion process results from natural defects of the sawlogs, the most important of which is curvature to some degree along the longitudinal axis. Since a large percentage of the logs obtained from the natural forests of North America, up to 40 % in some areas, falls in this particular category, sawmill technology has been striving for decades to cope with the problem of producing the maximum amount of merchantable lumber from crooked logs.
A first early technique consisted in hand guiding the piece through the cut by sidewise pressure, as visually determined by the operator, in order to conform with the observed form of the log or cant. As technical and mechanical advances took place from the early seventies onward, a rapid rise in feed capabilities occurred with the result that hand guiding became no longer practical, nor possible in most cases. Subsequently, there was brought forward a full array of complex mechanical arrangements which can cause the raw workpiece to go through a multiple cutting process along the line of its natural curvature.
While these developments have been most useful and productive, they also required large investments in specialized guiding equipment, either to be added to the infeeding system or to be incorporated into the production unit.